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  • Artikel: DFG Deutsche Nationallizenzen  (39)
  • 1995-1999  (28)
  • 1990-1994  (11)
  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3859-3864 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: To understand the nature of resonant tunneling in triple-barrier/double-quantum-well structures, we have investigated the properties of transmission probability TT of such structures with use of the transfer-matrix method. The transfer matrix of the middle barrier is calculated to analyze the amplitude decay, the phase shift, and the coupling effects that are induced between the two quantum wells. The dependencies of TT and the splitting of the resonant peaks on the middle-barrier thickness, the well width, and the symmetry of the structures are calculated. The origin of the transmission resonance and the resonant condition for symmetric (equal well widths) and asymmetric structures are discussed. The variations of TT with the applied voltage are also analyzed. The calculation results lead to some suggestions on how to design triple-barrier structures with improved performance.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2500-2502 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have investigated the resonant tunneling feature variations with temperature in molecular beam epitaxy grown strained Si0.78Ge0.22/Si double-barrier structures with different well width w and spacer thickness LS. Both w and LS have strong effects on the temperature characteristics of the peak current JP, the valley current JV, and the current peak-to-valley ratio (PVR). When w is reduced, both JP and JV are greatly increased. The resonant tunneling devices (RTDs) also have better temperature stability and PVR decreases slower. The RTD with larger LS has higher peak current. Beside w and LS, the quasi-Fermi level position has a very important influence on the resonant tunneling feature variations, which is stressed in the present work.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3365-3369 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A new approach to analyze the transport characteristics of resonant tunneling structures has been developed. It is shown that the Fermi-level Ef position per se, the temperature variations of the Fermi-level, the effective mass, and the mobility, have important influences on the resonant tunneling transport properties. Both calculations and experiments have shown very different features for heavy-hole and light-hole resonant tunneling in SiGe/Si resonant tunneling structures. These different features can for the first time be explained coherently. The calculated subband energy at current resonance can be much higher or lower than the Fermi level and the peak current can decrease or increase with temperature, depending on the device structure, the carrier type, and the working conditions. The calculations have predicted an interesting result that, in the low-temperature region, the valley current for the first heavy-hole resonance decreases with temperature, and that is confirmed by our experiments. The calculated temperature dependences of heavy- and light-hole transport, such as peak and valley currents/voltages and their variations with the well width, agree very well with our observations and other published results.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 738-740 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Temperature effects on current transport and the negative differential resistance for SiGe/Si and GaAlAs/GaAs resonant tunneling structures (RTS) have been studied, and the maximum working temperature Tm has been estimated. The calculations show that decreases in the carrier effective mass, well width and barrier thicknesses, lead to better temperature characteristics, implying higher peak current and larger peak-to-valley ratio (PVR) at higher temperature. These results are consistent with our experiment on SiGe/Si RTSs and other published experiments. The crucial role of nonresonant tunneling current Jnon in temperature effects for current transport is emphasized. Suggestions for optimizing RTS design to increase its Tm and PVR are discussed.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 3630-3635 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The growth of pinhole-free epitaxial DySi2−x films on atomically clean Si(111) has been achieved by depositing a 2-nm-thick Dy layer onto Si(111) with a 1.5-nm-thick capping amorphous Si (a-Si) layer at room temperature followed by annealing at 700 °C in ultrahigh vacuum. The thickness of the a-Si was selected to be such that the consumption of Si atoms from the substrate is minimized by taking into account the formation of an amorphous interlayer at the Dy/Si(111) interface. Based on our experimental findings, a new mechanism for the formation of pinhole is proposed. The Stranski–Krastanov growth behavior of epitaxial DySi2−x on Si(111) by solid phase epitaxy leads to the apparently random formation of a high density of recessed regions at the initial stage of silicidation. Polycrystalline DySi2−x was found to be present at the areas inside and epitaxial DySi2−x outside the recessed regions. Large numbers of Si atoms from the substrate can therefore diffuse through the recessed regions. As a result, the depth and size of the recessed regions increase with annealing time. Finally, the DySi2−x thin layer inside the recessed regions with higher interface energy is thermally unstable and breaks apart to form pinholes. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7653-7657 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The dominant diffusing species in the formation of amorphous interlayer between Gd and Si thin films have been determined by a Mo cluster marker experiment. Multilayered metal thin films were deposited on (001) Si in an ultrahigh vacuum electron beam evaporator. The positions of the Mo cluster markers relative to the Si substrate, before and after heat treatment, were determined by transmission electron microscopy and energy dispersive x-ray as well as autocorrelation function analysis. The displacement of the Mo cluster markers in the amorphous interlayer during the Gd–Si interdiffusion indicates that Si atoms constitute the dominant diffusing species during the growth of the amorphous interlayer. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 6083-6087 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The growth kinetics of amorphous interlayer (a-interlayer) formed by solid-state diffusion in ultrahigh vacuum deposited polycrystalline Gd thin films on (001)Si have been investigated by cross-sectional transmission electron microscopy. The growth of the a-interlayer was found to follow a linear growth law initially. The growth then slows down and deviates from a linear growth law. The result clearly indicated that the growth at early stage is consistent with an interface-reaction-controlled growth model rather than diffusion limited. The activation energy of the linear growth and maximum thickness of the a-interlayer were measured to be about 0.37 eV and 6.6 nm, respectively. Following the growth of amorphous interlayer, epitaxial hexagonal GdSi2−x was found to form at the a-interlayer/(001)Si interface at 225 °C. The relatively small lattice mismatch between GdSi2−x and (001)Si compared to other RESi2−x (RE=rare-earth metal) and (001)Si systems facilitates the epitaxial growth of GdSi2−x on (001)Si, which in turn hampers the further growth of a-interlayer. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 545-547 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The oxide superconductor Bi1.7Pb0.3Sr2−xAgxCa2Cu3Oy has been synthesized under the ordinary pressure. The x-ray diffraction spectra of these specimens show the presence of only 2212 phase when x〈0.4, and the transition temperature achieved 99 K. With the x increase, the structure of sample transfers to 2223 phase. The investigation indicates that substitution of Sr2+ by Ag1+ increases the distance between layers. This may respond to Tc increase in 2212 phase and 2223 phase form at a relatively low temperature. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Biochemistry 31 (1992), S. 8384-8388 
    ISSN: 1520-4995
    Quelle: ACS Legacy Archives
    Thema: Biologie , Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of the American Chemical Society 113 (1991), S. 4698-4700 
    ISSN: 1520-5126
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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